Tinnitus describes a perceived sound, e.g., ringing, buzzing, whistling, or roaring, that is experienced by a tinnitus sufferer and that does not exist as a physical sound. The condition can be annoying or very painful, and the discomfort caused by tinnitus frequently interferes with a sufferer's sleep. Tinnitus may occur at a specific frequency or over a small frequency range and is frequently constant; however, the specific frequency or small frequency range varies from patient to patient.